1. Field of the Invention
The present invention relates to control which improves the reliability of a compressor in a refrigerating cycle apparatus with a heating operation mode and defrosting operation mode.
2. Discussion of Background
In FIGS. 11 and 12 are shown a refrigerant circuit diagram of a conventional refrigerating cycle apparatus shown in e.g. JP-A-58115235 and a timing chart of the speed of rotation and the defrosting signal for the compressor in the refrigerating cycle apparatus. In FIG. 11, reference numeral 1 designates a compressor driven by a compressor motor, reference numeral 2 designates a four-way valve as a directional control valve for reversing the flow of a refrigerant, reference numeral 3 designates an indoor heat exchanger, reference numeral 4 designates a pressure reducing device such as a capillary tube, and reference numeral 5 designates an outdoor heat exchanger. The four-way valve, the indoor heat exchanger, the pressure reducing device and the outdoor heat exchanger are connected to the compressor 1 as a closed circuit to constitute the refrigerating cycle apparatus. Reference numeral 6 designates an indoor fan provided to confront the indoor heat exchanger 3, and reference numeral 7 designates an outdoor fan provided to confront the outdoor heat exchanger.
When the compressor motor drives the compressor 1 at a cooling mode in the refrigerating cycle apparatus, the refrigerant which has been compressed by the compressor 1 is cooled to be condensed by air supply from the outdoor fan 7 at the outdoor heat exchanger 5, is depressurized by the pressure reducing device 4 and evaporates at the indoor heat exchanger 3 to perform a cooling function. The indoor fan 6 supplies cooled air to cool the inside of a room. On the other hand, at a heating mode, the four-way valve 2 is switched to an on position as shown in FIG. 11 to reverse the flow of refrigerant, flowing the refrigerant in the order of the compressor 1, the four-way valve 2, the indoor heat exchanger, the pressure reducing device 4 and the outdoor heat exchanger 5. The indoor fan 7 supplies heated air to carry out the heating operation.
It has been widely known that the compressor is controlled by adjusting the frequency or the voltage of the power source for the compressor motor with an inverter controller though not shown. In this case, a desired speed of rotation is found based on a room temperature, a set value of the room temperature, an outdoor air temperature and so on, an automatic control is carried out to accommodate variations in load. If frost is formed on the outdoor heat exchanger during the heating mode, a defrosting operation is carried out.
Now, the defrosting operation of the outdoor heat exchanger during the heating mode will be explained in reference to the timing chart of FIG. 12. The defrosting signal in FIG. 12 contains a signal which is outputted based on a signal from a defrosting timer which is built in a microcomputer and operates at a certain period of time, and a temperature data signal from a defrosting thermostat and the like for detecting the temperature of the outdoor heat exchanger. For example, provided that the defrosting timer operates so as to carry out the heating operation for 50 minutes and the defrosting operation for 10 minutes in a period of 60 minutes, and that the defrosting thermostat outputs a signal indicative of defrosting completion at a temperature not less than 10.degree. C. and a signal indicative of frosting at a temperature not higher than -2.5.degree. C., the defrosting signal is outputted so as to commence defrosting at an AND condition of the defrosting timer and the defrosting thermostat and to complete defrosting at an OR condition of the defrosting timer and the defrosting thermostat.
In other words, when the defrosting thermostat detects a temperature higher than 10.degree. C. or 10 minutes for the defrosting operation has passed, the defrosting operation is completed and the apparatus returns to the heating operation. For example, when the defrosting timer reaches an A point, the microcomputer and the inverter controller are activated to increase the speed of rotation the compressor motor to the maximum value, keeping the heating operation. At a B point after lapse of a T1 period of time since the A point, a defrosting signal indicative of switching the four-way valve to an off position (cooling position) is outputted to switch the four-way valve, commencing the defrosting operation. During the defrosting operation, the compressor motor is rotated at the maximum value.
When the signal indicative of defrosting completion is outputted at a C point for completion of the defrosting operation, the microcomputer is activated to output a signal indicative of switching the four-way valve from the cooling position to the heating position, switching the four-way valve. However, the compressor motor is driven at the maximum speed of rotation for a T2 period of time after that, and returns to a normal set speed of revolution, continuing the heating operation.
As clearly seen from the explanation above, the prior art has increased the speed of rotation of the compressor to a value greater than the set speed of rotation calculated based on a room temperature and a set room temperature during the defrosting operation and certain periods of time before and after the defrosting operation.
Since the conventional refrigerating cycle apparatus has been constructed as stated earlier, an increase in the speed of rotation of the compressor from a normal set speed of rotation during the defrosting operation and after the defrosting operation causes a lubricating oil in the compressor to be taken out of the compressor housing at a large amount after defrosting. If the room temperature is near to a set temperature, the compressor is rotated at a low speed operation. If the compressor carries out such a low speed operation in a low outdoor air temperature state requiring the defrosting operation, the lubricating oil which has been taken out of the compressor housing becomes difficult to be recovered into the compressor due to a decrease in the current speed of the refrigerant, creating a problem in that the amount of the lubricating oil in the compressor housing reduces to degrade the reliability of the compressor.
Although it has been recently known that an HFC refrigerant (R410A, R407C, R32 etc.) and a lubricating oil of alkylbenzene are used in the refrigerating cycle apparatus, the lubricating oil which has been taken out becomes more difficult to be recovered into the compressor than the prior art apparatus since the mutual compatibility between the refrigerant and the lubricating oil in this case is lower than a combination of a conventional HCFC refrigerant (R22) and a lubricating oil of mineral oil or alkylbenzene.